Part One of the work comprises a systematic and in-depth study, insofar as the remaining documents allow, of all the delousing gas chambers and other disinfestation installations, in order to describe their characteristics and operation. The aim of this presentation is to demonstrate the rudimentary nature of the delousing gas chambers and the gradual increase in their area and volume. We pass from a fully planned complex of nineteen 10m³ chambers of the Degesch type built by Boos in the Stammlager to those of 490m³ rapidly improvised by the Bauleitung in Birkenau BW 5a and 5b. As the existence of these last is confirmed by Bauleitung drawings and the fact that they can still be seen in buildings BW 5a and 5b, their bluish walls bearing indisputable witness to their use with a hydrocyanic product, Zyklon-B, it is thus proven that the use of two underground morgues, each of 525m³, the Leichenkeller I of Krematorien II and III, as homicidal gas chambers presents no physical or technical impossibilities. The execution gas chambers in the United States are extremely sophisticated, but their design must be seen in the context of a highly technological country in peacetime, and they are presumably intended to be humane, which was not a prime concern of the SS. The presence of the delousing gas chambers also establishes that Zyklon-B, delivered by Tesch and Stabenow and by Degesch, was by no means destined solely for extermination purposes, but by far the greatest part of it was used for “Schädlingsbekämpfung” or pest control, both in these chambers and also in situ in the prisoners' accommodation blocks.

The Bauleitung SS used three different words to distinguish clearly between the methods of “disinfestation” used in their sanitary buildings. Each word has a very precise meaning and applies to a single type of procedure:

“Entwesung / Disinfestation": destruction of pests (essentially lice) by dry heat in hot air chambers. This technique makes it possible to destroy the majority of pathogenic germs (and harmful insects), without going as far as the stage of disinfection (total destruction of pathogenic germs) nor as far as sterilization (destruction of all micro-organisms, pathogenic or not);

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“Desinfektion / disinfection": the complete destruction of parasites and pathogenic micro-organisms in prisoners' effects using steam under pressure in autoclaves (very close to sterilization, but less complete).